1. Field
Orthopedic tools especially for removing damaged prosthetic acetabular cups.
2. Related Application
Applicant claims the benefit of provisional application No. 61/751,656, filed 11 Jan. 2013 and International application No. PCT/US2014/011325.
3. General Background and State of the Art
Total hip replacement surgery in which the hip joint is replaced by a prosthetic implant is a common orthopedic procedure. It is usually performed to relieve arthritis pain or because of hip fracture. Total hip replacements use two components, a femoral stem and an acetabular socket or cup. To insert the femoral stem, a surgeon removes the proximal end of the femur and shapes the end to receive the stem. The stem also has a ball or femoral head attached. Titanium, cobalt chromium and stainless steel are the most common stem materials. Metal or ceramic materials are common for the head.
The surgeon also removes cartilage and bone from the hip socket and then secures a prosthetic acetabular cup or socket into the hip socket using friction, cement or ingrowth material. Some acetabular cups are one piece; others are modular. They usually are high-density polyethylene or metal.
Most total hip replacements work very well. However, problems can arise especially many years after the surgery when the patient outlives the replacement. Those problems are more common when young adults have hip replacements following athletic injuries or accidents. However, persons who have hip replacements when they are older also can outlive their hip replacements. Then the patient may need a second hip replacement. A third hip replacement may be required in some circumstances.
When a surgeon preforms a second or third hip replacement, he or she must remove the existing acetabular cup. All methods for removing it are manual. One device for removing the acetabular cup is the Explant® acetabular cup removal system, sold by Zimmer, Inc. See http://www.zimmer.com/content/pdf/en-US/Explant_Acetabular_Cup_Removal_System_Surgical_Technique_%2897-7255-206-00%29%2810_2011%29.pdf (accessed Aug. 21, 2012). It includes a shank with an alignment head at the distal end. The head fits into the existing acetabular cup. A strong, rigid, curved blade, which is sized to conform to the acetabular cup, mounts to a fitting on the shank. The blade is spaced from the shank to fit between the outside of the acetabular cup and the hipbone. The surgeon works the blade between the acetabular cup and the hipbone until the blade is inserted to its maximum. The device also has a handle perpendicular to the shank. After the blade is fully inserted into the acetabular cup, the surgeon applies force to the handle to rotate the blade causing the blade to move along the bone/acetabular cup interface until it travels fully about the acetabular cup. That releases the acetabular cup for removal by the surgeon.
This technique is time consuming. An hour is common just for this preliminary work. Minimizing time in surgery especially under anesthesia is usually desirable. In addition, the hipbone behind the acetabular cup is thin. Especially for patients with osteoporosis, the force used with this technique can damage the hipbone.